• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.763-764
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• 2013

A three-dimensional image capturing device and its signal processing algorithm and apparatus are presented. Three dimensional information is one of emerging differentiators that provides consumers with more realistic and immersive experiences in user interface, game, 3D-virtual reality, and 3D display. It has the depth information of a scene together with conventional color image so that full-information of real life that human eyes experience can be captured, recorded and reproduced. 20 Mega-Hertz-switching high speed image shutter device for 3D image capturing and its application to system prototype are presented[1,2]. For 3D image capturing, the system utilizes Time-of-Flight (TOF) principle by means of 20MHz high-speed micro-optical image modulator, so called 'optical resonator'. The high speed image modulation is obtained using the electro-optic operation of the multi-layer stacked structure having diffractive mirrors and optical resonance cavity which maximizes the magnitude of optical modulation[3,4]. The optical resonator is specially designed and fabricated realizing low resistance-capacitance cell structures having small RC-time constant. The optical shutter is positioned in front of a standard high resolution CMOS image sensor and modulates the IR image reflected from the object to capture a depth image (Figure 1). Suggested novel optical resonator enables capturing of a full HD depth image with depth accuracy of mm-scale, which is the largest depth image resolution among the-state-of-the-arts, which have been limited up to VGA. The 3D camera prototype realizes color/depth concurrent sensing optical architecture to capture 14Mp color and full HD depth images, simultaneously (Figure 2,3). The resulting high definition color/depth image and its capturing device have crucial impact on 3D business eco-system in IT industry especially as 3D image sensing means in the fields of 3D camera, gesture recognition, user interface, and 3D display. This paper presents MEMS-based optical resonator design, fabrication, 3D camera system prototype and signal processing algorithms.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.276-279
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• 2004

Plasma enhanced chemical vapor deposition (PECVD) of silicon nitride (SiN) is a proven technique for obtaining layers that meet the needs of surface passivation and anti-reflection coating. In addition, the deposition process appears to provoke bulk passivation as well due to diffusion of atomic hydrogen. This bulk passivation is an important advantage of PECVD deposition when compared to the conventional CVD techniques. A further advantage of PECVD is that the process takes place at a relatively low temperature of 300t, keeping the total thermal budget of the cell processing to a minimum. In this work SiN deposition was performed using a horizontal PECVD reactor system consisting of a long horizontal quartz tube that was radiantly heated. Special and long rectangular graphite plates served as both the electrodes to establish the plasma and holders of the wafers. The electrode configuration was designed to provide a uniform plasma environment for each wafer and to ensure the film uniformity. These horizontally oriented graphite electrodes were stacked parallel to one another, side by side, with alternating plates serving as power and ground electrodes for the RF power supply. The plasma was formed in the space between each pair of plates. Also this paper deals with the fabrication of multicrystalline silicon solar cells with PECVD SiN layers combined with high-throughput screen printing and RTP firing. Using this sequence we were able to obtain solar cells with an efficiency of 14% for polished multi crystalline Si wafers of size 125 m square.

• Journal of Biomedical Engineering Research
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• v.40 no.5
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• pp.143-150
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• 2019

To evaluate the toxicity of ophthalmic drug, the Draize test and Bovine Corneal Opacity and Permeability (BCOP) test commonly used. In Draize test, experimental animals were under stress and pain due to long-term exposure of drug. In addition, regarding physiological functions, animal model is not perfectly reflected a human eye condition. Although some models such as $EpiOcular^{TM}$, HCE model, LabCyte Cornea-Model, and MCTT $HCE^{TM}$ were already presented advanced cornea ex-vivo model to replace animal test. In this sense, cornea tissue structure mimicked ex-vivo toxicity model was fabricated in this study. The corneal epithelial cells (CECs) and keratocytes (CKs) isolated from rabbit eyeball were seeded on non-patterned silk film (n-pSF) and patterned silk film (pSF) at $32,500cells/cm^2$ and $6,500cells/cm^2$. Sequentially, n-pSF and pSF were stacked to mimic a multi-layered stroma structure. The thickness of films was about $15.63{\mu}m$ and the distance of patterns was about $3{\mu}m$. H&E stain was performed to confirm the cell proliferation on silk film. F-actin of CKs was also stained with Phalloidin to observe the cytoskeletal alignment along with patterns of the pSF. In the results, CECs and CKs were shown the good cell attachment on the n-pSF and pSFs. Proliferated cells expressed the specific phenotype of cornea epithelium and stroma. In conclusion, we successfully established the ex-vivo cornea toxicity model to replace the eye irritation tests. In further study, we will set up the human ex-vivo cornea toxicity model and then will evaluate the drug screening efficacy.

• Korean Journal of Materials Research
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• v.29 no.6
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• pp.392-397
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• 2019

A cold roll-bonding process is applied to fabricate an AA6061/AA5052/AA6061 three-layer clad sheet. Two AA6061 and one AA5052 sheets of 2 mm thickness, 40 mm width, and 300 mm length are stacked, with the AA5052 sheet located in the center. After surface treatment such as degreasing and wire brushing, sample is reduced to a thickness of 1.5 mm by multi-pass cold rolling. The rolling is performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 400 mm at rolling speed of 6.0 m/sec. The roll bonded AA6061/AA5052/AA6061 complex sheet is then hardened by natural aging(T4) and artificial aging(T6) treatments. The microstructures of the as-roll bonded and age-hardened Al complex sheets are revealed by optical microscopy; the mechanical properties are investigated by tensile testing and hardness testing. After rolling, the roll-bonded AA6061/AA5052/AA6061 sheets show a typical deformation structure in which grains are elongated in the rolling direction. However, after T4 and T6 aging treatment, there is a recrystallization structure consisting of coarse equiaxed grains in both AA5052 and AA6061 sheets. The as roll-bonded specimen shows a sandwich structure in which an AA5052 sheet is inserted into two AA6061 sheets with higher hardness. However, after T4 and T6 aging treatment, there is a different sandwich structure in which the hardness of the upper and lower layers of the AA6061 sheets is higher than that of the center of the AA5052 sheet. The strength values of the T4 and T6 age-treated specimens are found to increase by 1.3 and 1.4 times, respectively, compared to that value of the starting material.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.12
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• pp.1011-1018
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• 2021

This numerical study conducts the modeling and the hover performance analyses of coaxial co-rotating rotor(or stacked rotor), using a rotorcraft comprehensive analysis code, CAMRAD II. The important design parameters such as the index angle and axial spacing for the coaxial co-rotating rotor are varied in this simulation study. The coaxial co-rotating rotor is trimmed using the torque value of the upper rotor of the previous coaxial counter-rotating rotor or the total thrust value of the previous coaxial counter-rotating rotor in hover. The maximum increases in the rotor thrust is 1.84% for the index angle of -10° when using the torque trim approach. In addition, the maximum decreases in the rotor power is 4.53% for the index angle of 20° with the thrust trim method. Thus, the present study shows that the hover performance of the coaxial co-rotating rotor for e-VTOL aircraft can be changed by the index angle.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.161-167
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• 2022

A cold roll-bonding process is applied to fabricate an AA6061/AA5052/AA6061/AA5052 layered sheet. Two AA6061 and one AA5052 sheets of 2mm thickness, 40mm width and 300mm length are alternately stacked, then reduced to a thickness of 2.0 mm by multi-pass cold rolling after surface treatment such as degreasing and wire brushing. The rolling is performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 400 mm at a rolling speed of 6.0 m/sec. The roll-bonded AA6061/AA5052/AA6061/AA5052 layered sheet is then hardened by natural aging (T4) and artificial aging (T6) treatments. The microstructure of the as-roll bonded and the age-hardened Al sheets was revealed by SEM observation; the mechanical properties were investigated by tensile testing and hardness testing. After T4 and T6 aging treatment, the specimens had a recrystallization structure consisting of coarse equiaxed grains in both AA5052 and AA6061 regions. The as-roll-bonded specimen showed a clad structure in which the hardness of AA5052 regions was higher than that of AA6061 regions. However, after T4 and T6 aging treatment, specimens exhibited different structures, with hardness of AA6061 regions higher than that of AA5052 regions. Strengths of T6 and T4 age-treated specimens were found to increase by 1.55 and 1.36 times, respectively, compared to the value of the starting material.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.400-406
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• 2024

Next-generation wide-bandgap semiconductors such as SiC, GaN, and Ga2O3 are being considered as potential replacements for current silicon-based power devices due to their high mobility, larger size, and production of high-quality wafers at a moderate cost. In this study, we investigate the gradual modulation of chemical composition in multi-stacked metal oxide semiconductor thin films to enhance the performance and bias stability of thin-film transistors (TFTs). It demonstrates that adjusting the Ga ratio in the indium gallium oxide (IGO) semiconductor allows for precise control over the threshold voltage and enhances device stability. Moreover, employing multiple deposition techniques addresses the inherent limitations of solution-processed amorphous oxide semiconductor TFTs by mitigating porosity induced by solvent evaporation. It is anticipated that solution-processed indium gallium oxide (IGO) semiconductors, with a Ga ratio exceeding 50%, can be utilized in the production of oxide semiconductors with wide band gaps. These materials hold promise for power electronic applications necessitating high voltage and current capabilities.

• Membrane Journal
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• v.27 no.2
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• pp.167-181
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• 2017

Graphene-based materials have been considered as a promising membrane material, due to its easy processability and atomic thickness. In this study, we studied on gas permeation behavior in few-layered GO membranes prepared by spin-coating method. The GO membrane structures were varied by using different GO flake sizes and GO solutions at various pH levels. The GO membranes prepared small flake size show more permeable and selective gas separation properties than large one due to shortening tortuosity. Also gas transport behaviors of the GO membranes are sensitive to slit width for gas diffusion because the pore size of GO membranes ranged from molecular sieving to Knudsen diffusion area. In particular, due to the narrow pore size of GO membranes and highly $CO_2$-philic properties of GO nanosheets, few-layered GO membranes exhibit ultrafast and $CO_2$ selective character in comparison with other gas molecules, which lead to outstanding $CO_2$ capture properties such as $CO_2/H_2$, $CO_2/CH_4$, and $CO_2/N_2$. This unusual gas transport through multi-layered GO nanosheets can explain a unique transport mechanism followed by an adsorption-facilitated diffusion behavior (i.e., surface diffusion mechanism). These findings provide the great insights for designing $CO_2$-selective membrane materials and the practical guidelines for gas transports through slit-like pores and lamellar structures.

• Economic and Environmental Geology
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• v.44 no.3
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• pp.229-238
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• 2011

S-wave, which provides lithology and pore fluid information, plays a key role in estimating gas-hydrate saturation. In general, P- and S-wave velocities increase in the presence of gas-hydrate and the P-wave velocity decreases in the presence of free gas under the gas-hydrate layer. Whereas there are very small changes, even slightly increases, in the S-wave velocity in the free gas layer because S-wave is not affected by the pore fluid when propagating in the free gas layer. To verify those velocity properties of the BSR (bottom-simulating reflector) depth in the gas-hydrate prospect area in the Ulleung Basin, P- and S-wave velocity profiles were derived from multi-component ocean-bottom seismic data which were acquired by Korea Institute of Geoscience and Mineral Resources (KIGAM) in May 2009. OBS (ocean-bottom seismometer) hydrophone component data were modeled and inverted first through the traveltime inversion method to derive P-wave velocity and depth model of survey area. 2-D multichannel stacked data were incorporated as an initial model. Two horizontal geophone component data, then, were polarization filtered and rotated to make radial component section. Traveltimes of main S-wave events were picked and used for forward modeling incorporating Poisson's ratio. This modeling provides S-wave profiles and Poisson's ratio profiles at every OBS site. The results shows that P-wave velocities in most OBS sites decrease beneath the BSR, whereas S-wave velocities slightly increase. Consequently, Poisson's ratio decreased strongly beneath the BSR indicating the presence of a free gas layer under the BSR.

• Journal of Energy Engineering
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• v.20 no.3
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• pp.185-190
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• 2011

This paper describes design, fabrication, and evaluation of the conduction cooled high temperature superconducting (HTS) magnet for superconducting magnetic energy storage (SMES). The HTS magnet is composed of twenty-two of double pancake coils made of 4-ply conductors that stacked two Bi-2223 multi-filamentary tapes with the reinforced brass tape. Each double pancake coil consists of two solenoid coils with an inner diameter of 500 mm, an outer diameter of 691 mm, and a height of 10 mm. The aluminum plates of 3 mm thickness were arranged between double pancake coils for the cooling of the heat due to the power dissipation in the coil. The magnet was cooled down to 5.6 K with two stage Gifford McMahon (GM) cryocoolers. The maximum temperature at the HTS magnet in discharging mode rose as the charging current increased. 1 MJ of magnetic energy was successfully stored in the HTS magnet when the charging current reached 360A without quench. In this paper, thermal and electromagnetic behaviors on the conduction cooled HTS magnet for SMES are presented and these results will be utilized in the optimal design and the stability evaluation for conduction cooled HTS magnets.